The invention relates to a method for producing a cavity to receive an acetabulum in a navigated pelvic bone with the aid of a navigated tool.
During implantation of an artificial hip joint, an artificial acetabulum is inserted into the pelvic bone, and for this a cavity that receives the acetabulum must be machined in an anatomically defined orientation into the pelvic bone at the anatomically defined location. These cavities are normally hemispherical and are generated by means of a hemispherical milling cutter. To be able to determine and maintain the precise disposition—i.e. the orientation and position—of the receiving cavity, it is known to navigate the pelvic bone as well as the tool generating the cavity by means of a surgical navigation system. Such a navigation system enables the relative spatial coordination of the tool and the pelvic bone to be determined and monitored.
When replacing a defective acetabulum with an artificial acetabulum, the acetabulum is normally implanted at substantially the same location as that where the natural acetabulum was previously arranged, this position being referred to hereafter as the primary acetabulum.
However, there are also cases in which the natural acetabulum is not situated in the anatomically desirable position, whether as a result of a congenital defect or as a result of the natural joint socket being displaced out of the position of the primary acetabulum, usually upwards, i.e. in the cranial direction. In these cases it is extraordinarily difficult when implanting an artificial joint socket that is to be inserted at the anatomically normal position, i.e. in the position of the primary acetabulum, to determine this position on the pelvic bone, so that the tool can then be guided in the desired manner.